﻿using System;
using System.Collections.Generic;

namespace Priority_Queue
{
    /// <summary>
    ///     The IPriorityQueue interface.  This is mainly here for purists, and in case I decide to add more implementations
    ///     later.
    ///     For speed purposes, it is actually recommended that you *don't* access the priority queue through this interface,
    ///     since the JIT can
    ///     (theoretically?) optimize method calls from concrete-types slightly better.
    /// </summary>
    public interface IPriorityQueue<TItem, in TPriority> : IEnumerable<TItem>
        where TPriority : IComparable<TPriority>
    {
        /// <summary>
        ///     Returns the head of the queue, without removing it (use Dequeue() for that).
        /// </summary>
        TItem First { get; }

        /// <summary>
        ///     Returns the number of nodes in the queue.
        /// </summary>
        int Count { get; }

        /// <summary>
        ///     Enqueue a node to the priority queue.  Lower values are placed in front. Ties are broken by first-in-first-out.
        ///     See implementation for how duplicates are handled.
        /// </summary>
        void Enqueue(TItem node, TPriority priority);

        /// <summary>
        ///     Removes the head of the queue (node with minimum priority; ties are broken by order of insertion), and returns it.
        /// </summary>
        TItem Dequeue();

        /// <summary>
        ///     Removes every node from the queue.
        /// </summary>
        void Clear();

        /// <summary>
        ///     Returns whether the given node is in the queue.
        /// </summary>
        bool Contains(TItem node);

        /// <summary>
        ///     Removes a node from the queue.  The node does not need to be the head of the queue.
        /// </summary>
        void Remove(TItem node);

        /// <summary>
        ///     Call this method to change the priority of a node.
        /// </summary>
        void UpdatePriority(TItem node, TPriority priority);
    }
}